This invention relates to a water jet propulsion unit and more particularly to an improved jet propulsion unit particularly useful in propelling watercraft.
The advantages of jet propelled watercraft are well known. It is also desirable, for a variety of reasons, to position the jet propulsion unit in a tunnel positioned on the underside of the watercraft hull. This provides a neat and smooth appearance. However, due to the ability of jet propelled watercraft to operate in shallow water and for a variety of other reasons, it is desirable to access the water inlet opening of the jet propulsion unit for servicing. Also, to avoid barnacle and other encrustation, it is desirable if the jet propulsion unit can be moved so that its water inlet opening is raised out of the water during times when the watercraft is not being operated. The copending application of Noburo Kobayashi, entitled "Water Jet Propulsion Unit," Ser. No. 489,361, filed March 1990, now abandoned, and assigned to the assignee of this application discloses several embodiments of improved water jet propulsion units wherein a tunnel mounted jet propulsion unit is pivotal about a transverse longitudinal axis and rotatable about a longitudinally extending axis so as to raise the water inlet opening out of the body of water in which the water craft is operating when not in use and also so as to permit accessing of the water inlet opening of the jet propulsion unit through an access opening in the hull.
Although the arrangement disclosed in that copending application is particularly useful in solving the problems attendant with normal jet propulsion unit mountings, there are certain improvements that can be made. For example, in one disclosed embodiment of the aforenoted copending application the rotational movement of the jet propulsion unit is achieved by an electric motor. However, the mounting of the electric motor within the tunnel can give rise to serious corrosion problems. Although that application also mentions the possibility of employing a hydraulic motor for the rotational movement, there is no disclosure of how the hydraulic motor could be interrelated with the other construction.
It is, therefore, a principal object of this invention to provide an improved arrangement for a water jet propulsion unit that is both pivotal about a transverse axis and rotatable about a longitudinal axis and wherein both movements are achieved by a hydraulic system including a pair of hydraulic motors.
It is a further object of this invention to provide a hydraulic system for operating a water jet propulsion unit of the described type from a single power source of hydraulic fluid.
It is also desirable to provide a seal between the water inlet opening of the jet propulsion unit and the hull of the watercraft. Such seals improve the efficiency of the jet propulsion unit and the performance of the watercraft. However, if a seal is employed this seal must accommodate the relative movements aforedescribed. If this is done and if the jet propulsion unit is rotated before it is pivoted, there is a possibility of damage to the seal.
It is, therefore, a further principal object of this invention to provide a jet propulsion unit for a watercraft that is mounted for pivotal movement about a transverse axis and rotary movement about a longitudinal axis and which is power operated for these movements and in which the pivotal movement must occur before rotary movement can be accomplished.
It is a further object of this invention to provide an improved control arrangement for controlling the pivotal and rotary movement of a jet propulsion unit so as to insure that the desired sequence of operation is achieved.
The advantages of employing hydraulic motors for operating the jet propulsion units and particularly their particular types of movements previously described has already been noted. However, the mounting of plural hydraulic motors can present substantial problems bearing in mind the small space available. The external mounting of a hydraulic motor for achieving the rotary movement can present substantial difficulties in this regard.
It is, therefore, a further object of this invention to provide an improved jet propulsion unit having rotatable segments and incorporating an integral hydraulic motor for achieving the rotary motion.